haptic rendering using simplification
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Haptic Rendering using Simplification. Comp259 Sung-Eui Yoon. Overview. Continuous-Adaptive Haptic Rendering Sensation Preserving Simplification. Haptic Rendering. 3 major steps Initializing the haptic device and transferring the dataset - PowerPoint PPT PresentationTRANSCRIPT
Haptic Rendering using Simplification
Comp259Sung-Eui Yoon
Overview Continuous-Adaptive Haptic
Rendering Sensation Preserving Simplification
Haptic Rendering 3 major steps
Initializing the haptic device and transferring the dataset
Collision detection between virtual objects and the probe
Estimating force• The force is fed to the generic probe
It require high update rates (1000Hz)
Haptic Rendering Process
Methods to reduce model complexity Spatial subdivision (octree, ..)
We may lose meaningful cell that can affect user.
User can perceive incorrect force when moving fast.
Static LOD Switching LOD may lead to noticeable
changes. There may be only one LOD for large model
Continuous-Adaptive Haptic Rendering It gives various level of detail at
different regions of the surface Also, reduce complexity of model
Doesn’t send whole geometry. Instead, send high resolution near the
probe. Based on View-Dependence Tree for
view-dependent rendering.
View-Dependent Simplification At preprocessing, calculate sequences of
edge collapses by model simplification method
From this, we can make a vertex hierarchy, which is represent the way how to simplify a model at run-time
View-Dependent Simplification
Switch Value• Quadric error between original geometry and
simplified one.• At run-time, we calculate projection error from this.
Dependency Information• Neighboring faces when performing collapse and
split to prevent foldover.
View-dependent Rendering Process active vertices list, which represent
current LOD of model Initialize active vertex node list with root nodes.
Reconstruction of a real-time adaptive mesh Need active triangle list There are frame-to-frame coherence
Result Image
Selecting LOD Assumption
Geometry close to probe has a higher probability of collision with the probe.
So, we need more higher resolution near the probe.
How to define appropriate resolution Bell-shaped filter, mapping table
between distance and switch value.
Run-time Algorithm Scan node of vertex list Compute the distance from the probe Determine switch value Compare this with the one stored in node
Split node if computed value is less than one in node and node satisfy dependency
Merge node with sibling if computed value is greater stored one of parent and the node meet dependency.
Optimizations Haptic and graphics buffers are updated
in an incremental fashion
The graphics and haptic rendering require different update rate 20Hz for graphics rendering 1000Hz for haptic rendering update geometry at 20 Hz
Result Use the GHOST API library.
It fails when it is pushed to run at less than 1000Hz.
Limitation Doesn’t present error metric for haptic
rendering Just use switch value for projection error.
Isn’t clear to integrate view-dependent simplification with other acceleration (Bounding Volume Hierarchy) technique for collision detection.
Sensation PreservingSimplification Key observation
Human haptic perception of geometric feature depend on the ratio between the contact area and the size of the feature
In visual rendering Consider surface deviation and the viewing
distance In haptic rendering
Contact surface area and the resolution of the simplified model
Design Issues Design multiresolution hierarchy
that : Minimize perceptible surface deviation
• Filtering the detail at appropriate resolution Reduce the polygonal complexity of low
resolution representations• Incorporating mesh decimation
Are themselves BVH of convex hull• The system take advantage of BVH of
convex hull
Definition of Resolution (Sampling) Resolution r
1D example: The inverse of the distance between two subsequent samples.
2D : the sampling resolution of an edge (v1, v2) of the mesh M at resolution, rj ,Mj
• can be estimated as the inverse of the projected length of the edge onto a low resolution representation of the mesh, Mi
Filtered Edge Collapse Two goals in the construction of
hierarchy. Generate the hierarchy with low polygonal
complexity at low resolution Filter details as we compute low resolution
These are achieved by merging downsampling and filtering operation
Convexity Constraints A surface convex decomposition for
collision detection must meet these constraints All the interior edge of a convex patch must
themselves be convex. No vertex in a convex patch may be visible
from any face except the ones incident on it The virtual face added to complete the convex
hull cannot intersect the mesh
Local Convexity Constraints
Global Convexity Constraints Too complicated to be incorporated
into filtering process Verified after the filtering
use bisection search between v3 and v3 if v3 meet the constraint
^
^
Multiresolution Hierarchy Generation Starting by computing an initial convex
decomposition and resolution for all the edges.
Edges are inserted in a priority queue with validity and resolution as 1st and 2nd keys for sorting.
Generating new LOD every time the number of convex pieces are halved. Combine neighboring convex pieces as long
as they represent a single valid convex patch.
Contact computation for Haptics Based on a penalty-based force
computation Force displayed is proportional to the
penetration depth. Bounding Volume Test Tree (BVTT)
Perform contact query as descending BVTT, which is dynamically constructed.
Generalized front tracking to exploit temporal coherence.
BVTT and generalized front tracking
Sensation Preserving Selective Refinement Only refine the lower node of BVTT if the
missing detail is perceptible. Perceptibility
Depends on magnitude of surface feature and contact area
Results
Reference M. Otaduy and M. Lin, “Sensation Preserving Simplification
for Haptic Rendering”, to be appeared in SIGGRPH2003 J. El-Sana, and A. Varshnewy, “Continuouly-Adaptive
Haptic Rendering”, Virtual Environments 2000 J.El Sana and A. Varshney. Generalized view-dependent
simplification, In Proceeding EUROGRAPHICS99, pages 83-94, 1999
M. Garland and P. Heckbert, “Surface simplification using quadric error metrics”. In Proceedings of SIGGRAPH ’97(Los Angeles, CA), pages 209 – 216. ACM SIGGRAPH, ACM Press, August 1997.
H. Hoppe, Progressive meshes, In Proceedings SIGGRAPH 96, pages 99-108. ACM SGIGGRAPH 1996